A standard tunneling machine has an automotive base typically provided with a track drive and having a turntable defining a vertical axis about which a main support is pivotal. This automotive base has a diesel engine that serves principally to pressurize hydraulic fluid used by all the motors and actuators of the machine. A cutter is carried at the front end of an arm having a back end pivoted about a horizontal axis on the main support, and the cutter may be tippable about the longitudinal axis of the arm also. A conveyor rides on the ground immediately behind the cutter to take in and conduct the rock ground from the face by the cutter back past the automotive machine base.
Such a machine drives a tunnel by cutting away the end face of the tunnel and conveying it back out of the way. The cutter is moved up and down and from side to side to make the tunnel whatever width and height are required.
As the tunnel is driven it is necessary to stabilize the tunnel walls, principally the roof. This is done by drilling deep blind holes in the wall, anchoring long rock bolts in them with an epoxy mixture and/or an expansion sleeve, and then pulling large fishplate washers against the face with nuts threaded over the projecting ends of the bolts. In this manner the rock of the wall, even if it has been loosened as the tunnel was driven, is secured solidly together and to the overlying undisturbed rock, greatly reducing likelihood of a cave-in.
The stabilizing or bolting apparatus, which normally comprises a drilling unit and a bolt-setting unit, is typically driven by the engine on the tunneling-machine base. In German Pat. document No. 3,334,975 each side of the base of the machine is provided with a bolting apparatus that can be maneuvered by respective actuators for three-dimensional movement. Thus quite some extra equipment, normally at least three double-acting hydraulic rams, must be provided for each drilling unit, considerable increasing the cost of the machine and the difficulty of controlling it.
Although the top of the drilling apparatus can move over quite some arc, it is still impossible to plant a bolt directly over the middle of the tunnel. The inner bolts must normally be set at an angle, and only the bolts set directly above the sides of the machine will be vertical and perpendicular to the face, which is the most effective position. What is more, with such an apparatus it is impossible to stabilize the tunnel roof until quite some time after it is excavated, that is long enough for the tunneling machine to have advanced the several meters from the cutter to the bolting devices. This unstabilized roof can therefore cave in onto the cutting machine, and generally creates a danger, particularly as it is immediately adjacent an area where the cutter is doing considerable violence to the rock.